This invention relates to a phosphor consisting of an alkaline earth halide and a rare earth fluoride and activated by europium.
It was customary in the past to use CaWO.sub.4 as a fluorescent material for forming an X-ray intensifying screen. Further, various fluorescent materials have been proposed to date for improving the sensitivity of the X-ray intensifying screen. For example, Canadian Pat. No. 896453 discloses an alkaline earth halide phosphor such as BaFCl:Eu. In this phosphor, however, it is difficult to add divalent europium as an activator even if firing is carried out under neutral or reducing conditions, resulting in that the produced phosphor tends to emit light shifting a longer wavelength side because of the presence of trivalent europium. In short, the alkaline earth halide phosphor of this type is defective in that a state firing condition is difficult to determine.